@@TRANCOUNT difference between SQL 7 and SQL 2000

During testing of an application, i noticed a difference between
SQL 2000 and SQL 7, both with identical config.

In a nutshell:
A table has a trigger for UPDATE and DELETE.
When a column in the table is UPDATED the following happens:

In autocommit mode, when entering a trigger the trancount equals
1 for both SQL 7 and 2000.

When the same update is performed in an explicit transaction
in SQL 7 @@TRANCOUNT equal 2, and in SQL 2000 @@TRANCOUNT equals 1.

Configuration is the same and there are no implicit transactions.

I don't need a work around as this will invalidate the migration
process as both products should behave identically.
What would influence the difference or why is there a difference???
Is there something which has been overlooked?

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The following code replicates the problem

Ensure implicit transactions are off in both versions at the server
level, thus defaulting to autocommitted mode.
Ensure sp_configure settings are identical.